1. Field of the Invention
This invention relates to an improved process for production of chlorinated trisodium phosphate. This process produces a product with a higher chlorine recovery efficiency and more stable chlorine content than prior art process.
2. Background Discussion
Chlorinated trisodium phosphate is used as a source of available chlorine for cleaning, bleaching, and sterilization. It is used as a component in cleansers, automatic dishwashing compositions, and similar applications and in pure form as a sterilizing agent in food processing plants, dairies, breweries, and the like.
The name "chlorinated trisodium phosphate" is actually a misnomer. It is currently believed to be a crystalline material consisting of Na.sub.3 PO.sub.4, Na.sub.2 HPO.sub.4, NaOCl, NaCl, and H.sub.2 O. The available chlorine is supplied by equal moles of NaOCl and NaCl. The name chlorinated trisodium phosphate remains for historical reasons and for the sake of simplicity is used herein.
Chlorinated trisodium phosphate is produced by adding a sodium hypochlorite solution to a hot sodium phosphate liquor, cooling the resulting mixture to produce crystals of the product either by crystallization from an aqueous solution or from a molten mass of chlorinated trisodium phosphate, and drying the crystals. During the course of this process, some of the chlorine added by the sodium hypochlorite solution may be lost. Additionally, some of the chlorine present in the final product does not react to produce available chlorine. The available chlorine that can be obtained from the chlorinated trisodium phosphate compared to the amount of chlorine present as hypochlorite and chloride, expressed in terms of percents, is called the chlorine recovery efficiency. The chlorine recovery efficiency in prior art processes is in the range of 75% to 80%. The chlorine recovery efficiency can be enhanced somewhat by use of additives, such as by the addition of a water soluble silicate to the mixture, see U.S. Pat. No. 3,656,890, Toy, et al.
It is an advantage of this invention that chlorinated trisodium phosphate is produced that has an increased percentage of available chlorine, an increased chlorine recovery efficiency, and more stable available chlorine, all without the use of additives. Further advantages will become apparent from the following description and examples.